Conventionally, there exists a battery apparatus that is obtained by connecting in parallel a plurality of storage batteries, each of which is includes a plurality of electric storage elements connected in serial to have the high voltage, so as to realize increase in capacity. In a case where the plurality of storage batteries is connected in parallel, when electric-storage states of the storage batteries are different from each other, there exists in this electric storage apparatus a risk that overcurrent flows from a storage battery having a high electric potential to a storage battery having a low electric potential, thereby leading to breakage.
Thus, there exists an electric storage apparatus in which storage batteries having small potential difference are connected in parallel when a plurality of storage batteries is to be connected in parallel and their electric potentials are equalized so as to suppress breakage caused by the above overcurrent (see Japanese Unexamined Patent Application Publication No. 2014-514692, for example).
However, in a conventional electric storage apparatus, there is not considered how to increase the number of parallel-connectable storage batteries when electric potentials of storage batteries are to be equalized.